Transspinal versus Epidural Stimulation for Exoskeletal Assisted Walking after Spinal Cord Injury

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Restoring locomotion following spinal cord injury (SCI) has been the focus of years of research aimed at ameliorating several of health-related comorbidities. Spinal cord epidural stimulation (SCES) exhibits the rehabilitation potential of restoring locomotion in individuals with SCI when combined with intensive locomotion training. Despite this potential, such protocols are likely impractical when applied across large clinical SCI populations due to high monetary costs. Similar to SCES, transspinal stimulation (TS) has also exhibited neuromodulatory benefits by externally stimulating lumbro-sacral neural circuity to generate step-like activities in persons with complete SCI; however, these techniques also require intense gait training. Recently robotic exoskeletons have been used as a promising tool to circumvent limitations associated with labor-intensive locomotor training, and have been safely used as an effective approach in improving levels of physical activity in persons with complete SCI. Recent work has demonstrated the benefits of combining EAW and neuromodulatory techniques. Following 12-weeks of EAW+SCES training, improvements in locomotion led researchers to decrease the amount of EAW swing assistance to 35% in a person with a C7 complete SCI. This was accompanied by 573 unassisted steps, which represents 50% of the total number of steps taken during that session. Electromyographic (EMG) activity also increased during both stance and swing phases, reflecting the individual’s ability to rhythmically fire paralyzed muscles during EAW+SCES. Additionally, cardio-metabolic loads were increased during exoskeletal stepping when combined with SCES as compared to stepping without SCES. The participant also showed a modest decrease in his total and regional absolute fat mass. These preliminary findings suggest that neuromodulation using SCES with exoskeletal ambulation may provide a feasible rehabilitation approach for persons with SCI. The goal of the current study is to examine and compare the effects of EAW combined with SCES or TS in persons with motor complete SCI. The data generated from this application will also enable larger clinal trials to explore ways to optimize exoskeletal assisted gait training through the use of different neuromodulation modalities with SCI. Following a repeated-measure design, 10 participants with chronic, motor complete (AIS A and B) SCI (age:18-60 years) will be randomly assigned to participate in either 6-months of EAW+SCES (n=5) or EAW+TS (n=5) training. The entire duration of the trial will be approximately 1 year for each participant. Initially, participants will undergo 3-months of EAW training (3 sessions/week), which will be followed by randomization into either a EAW+SCES group or EAW+TS group for an additional 6-months of training (both groups: 3 sessions/week) and a 3-month follow-up period for both groups. Measurements at baseline (BL: prior to EAW) and 4 post-intervention timepoints will occur every 3-months (P1: following 3-months of EAW; P2: following 3-months of EAW+TS or EAW+SCES; P3: after completing 6-months of EAW+TS or EAW+SCES; P4: 3-months after termination of EAW+TS or EAW+SCES). This pilot work will have 3 specific aims: Aim 1. We will determine and compare improvements to locomotor control following 6 months of EAW+TS and EAW+SCES as measured by 10-meter walking speed, the number of unassisted EAW steps, and EMG activity. Aim 2. We will determine and compare improvements to cardio-metabolic risk factors following 6 months of EAW+TS and EAW+SCES as measured by total and regional body composition, oxygen uptake, and fasting lipid profile. Aim 3. We will determine and compare improvements in bladder health following 6 months of EAW+TS and EAW+SCES as measured by bladder filling and emptying.